The present invention relates to a method for testing subscriber access lines, together with an associated subscriber line circuit and a connected subscriber terminal in a digital telecommunications system.
Until now, subscriber lines have been tested predominantly using central test facilities which are switched on by setting up a test connection to the relevant subscriber line. As such, these tests are carried out routinely only at relatively long time intervals, which are in the order of magnitude of weeks or even months. In practice, therefore, a very high percentage of faults which occur originate from customer complaints which, depending on the nature of the fault, are often made a considerable time after a fault was originally found. This makes it considerably more difficult to organize fault rectification as quickly as possible.
However, it is also already known for subscriber line circuits whose functions are at least partially provided by using a digital signal processor to use this digital signal processor for evaluating line parameters and, thus, for carrying out tests as well (European Patent Application 0 451 759 A3). In the case of the known solution, access points to the transmission path and to the reception path of the subscriber line are provided at which voltages occur during operation of the subscriber line circuit which are evaluated in different combinations to produce a specific test result.
Thus, here, the testing of subscriber access lines is localized and can be carried out online. Owing to the performance of modem digital signal processors, their utilization level is well below full load when carrying out subscriber access functions.
With the known test concept that has been mentioned, it is possible to carry out a number of different test functions to identify malfunctions virtually all the time, automatically and successively. The term virtually all the time encapsulates the difference between this and a continuous test determination, which results firstly from the fact that a digital signal processor (as mentioned) has another main task in this context and secondly from the fact that it is likewise responsible for a number of subscriber lines; therefore, being available to the individual lines only in the time-division multiplex mode.
Thus, as a rule, such integrated test systems allow faults in the subscriber access area to be identified and, depending on the nature of the fault, possibly even to be rectified before they have been noticed by the customer. An object of the present invention, therefore, is to utilize the capabilities of such an integrated test concept to further enhance customer usefulness.